[modern]
# Support for dynamic import is the main litmus test for serving modern builds.
# Although officially a ES2020 feature, browsers implemented it early, so this
# enables all of ES2017 and some features in ES2018.
supports es6-module-dynamic-import

# Exclude Safari 11-12 because of a bug in tagged template literals
# https://bugs.webkit.org/show_bug.cgi?id=190756
# Note: Dropping version 11 also enables several more ES2018 features
not Safari < 13
not iOS < 13

# Exclude unsupported browsers
not dead

[legacy]
# Legacy builds are transpiled to ES5 (strict mode) but also must support some features that cannot be polyfilled:
# - web sockets to communicate with backend
# - inline SVG used widely in buttons, widgets, etc.
# - custom events used for most user interactions
supports use-strict and supports websockets and supports svg-html5 and supports customevent